The objective of the project is to study te mechanisms of action of parathyroid hormone (PTH) focusing primarily on the role of cAMP, the effects of PTH on cell proliferation, and the development of a bioasssay based on stimulation of adenylte cyclase from osseous tissue. For establishing the PTH bioassay based on stimulation of osseous tissue adenylate cyclase, we propose to characterize the adenylate cyclase of the highly responsive osteosarcoma clone (ROS 17/2) with respect to: optimum assay conditions for maximizing hormone response (MgATP2-, Mg2+, GTP) and compare effects of PTH from various species as well as synthetic PTH fragments and analogs. We propose to investigate the role of the previously discovered adenylate cyclase enhancing cytosol factor (Egan et al., BBRC 80176-182, 1978) on hormone stimulation of the enzyme using: (1) Responsive and non responsive clones and (2) the parallel in vivo inducibility of cytosol factor and hormone response, as experimental tools. We propose to further characterize the growth stimulatory effect of PTH (PTE) on osteosarcoma cells and primary culture bone cells by measuring: (1) ornithine decarboxylase induction, (2) DNA synthesis (3HTdr incorporation), (3) growth curves (cell #) and (4) percent mitoses, as a function of hormone concentration and cell cycle parameters.